1. Field of the Invention
This invention relates to radionuclide-labeled biological substances useful in the fields of diagnosis and therapy and is more particularly related to metal-chelating compounds in which the donor atoms are nitrogen and sulfur.
2. Description of the Background
Radiolabeled compounds are important tools in medical diagnosis and treatment. Such compounds are employed in a variety of techniques including the diagnosis of deep venous thrombi, the study of lymph node pathology, and the detection, staging and treatment of neoplasms. A number of these compounds employ metal radionuclides such as technetium-99m. When employing radionuclides for in vivo administration, it is desirable that the radionuclide localize in a target organ or cancer site. Therefore, radionuclides are usually formulated to provide preferential binding to or absorption by the particular organ or tissue. There is considerable interest in being able to accurately direct a radionuclide to a preselected site to reduce background radiation directed to surrounding or distant tissue, reduce the dosage, minimize background for in vivo imaging, and minimize undesirable side effects. Toward this end, methods involving specific ligands or receptors to which the radionuclide may be conjugated are of interest.